The present invention relates to a varnish coater disposed between a printing unit and a delivery apparatus of a rotary press or in an independent coating unit to apply varnish on a printed surface.
The surface of paper printed by a rotary printing press is not quickly dried and can be contaminated in the subsequent processing. In a sheet-fed rotary printing press, offsetting tends to be caused when printed sheets are stacked. In order to solve these problems, conventionally, a dryer is arranged in a delivery path of the printed products, or a powder is sprayed on the printed paper surfaces. However, in this case, the dryer becomes large, and powder spraying results in surface roughening of the printed surface. Surface roughening tends to entail a loss of gloss and subsequent poor printing. Instead of these techniques, varnish is applied to the printed surface to prevent the surface from being contaminated and to give it gloss. Varnishing is performed in printed products such as covers of books, catalogs and pamphlets which require an aesthetic effect.
The varnish coater is used as an independent apparatus. However, recently, the varnish coater is generally disposed in a delivery path of a printing press to shorten a coating time and an associated operation time for restacking the printed sheets and hence to improve the coating efficiency. The varnish coater generally has rollers in the same manner as that of a dampening apparatus for dampening a surface of a plate mounted on a plate cylinder of the printing unit. Varnish stored in a varnish pan is supplied to a surface of a blanket cylinder through the rollers. The varnish is transferred to a sheet passing between the blanket cylinder and an impression cylinder.
However, the conventional varnish coater of this thick paper such as a cover. The blanket on the surface of the blanket cylinder is partially deformed to result in a nonuniform thickness of the varnish film. In this case, a thickness of an underlay inserted between the blanket and the metal surface of the blanket cylinder must be adjusted after the rotary printing press is stopped. When the rollers are stopped for a long period of time while the coating operation is interrupted, varnish is hardened and many wasted paper sheets are produced when the coating operation is restarted. In order to prevent this, the rollers inserted between the form roller and the varnish type has the following problem in contact pressure adjustment between the blanket cylinder and the form roller for transferring varnish to the blanket cylinder. During the coating operation, since the blanket cylinder is in sliding contact with the form roller which transfers varnish to the blanket cylinder, the contact pressure of the form roller with respect to the blanket cylinder must be properly adjusted to obtain a uniform thickness of the varnish film to be coated on the printed sheet. On the other hand, the coating operation is often performed for pan must be brought into sliding contact with the form roller. After the blanket cylinder is washed or cleaned, the underlay is adjusted. Subsequently, after the underlay is adjusted, the blanket cylinder is located in the throw-on position. In this case, in order to properly perform the coating operation, the form roller must be brought into tight contact with the blanket cylinder to transfer varnish from the form roller to the blanket cylinder before the blanket cylinder is located in the throw-on position. The adjusting condition is preferably checked. For this purpose, the contact pressure of the form roller with respect to the blanket cylinder must be properly adjusted even if the blanket cylinder is located in the throw-off position.
In this manner, the contact pressure of the form roller with respect to the blanket cylinder must be controlled for both the throw-on and throw-off positions of the blanket cylinder. Conventionally, the contact pressure is adjusted by a turnbuckle and an eccentric pin, or by stoppers for defining the pivotal range of the form roller support arm. In addition, the contact pressure adjustments are independently performed at the throw-on and throw-off times of the blanket cylinder. The contact pressure adjustment must be performed every time irregular thickness is eliminated or the blanket of the blanket cylinder is worn out, resulting in time-consuming operation. In addition to this disadvantage, since an impact occurs when the form roller is brought into tight contact with the blanket cylinder by means of the form roller arm, the durability of the component parts is degraded upon repetition of the above contact operation. Furthermore, when the contact pressure is adjusted at the throw-on and -off positions, the pressure adjusted at one of the positions influences that at the other, resulting in inconvenience.